The invention relates to stents and stent delivery and deployment assemblies for use at a bifurcation and, more particularly, one or more stents for repairing bifurcations, blood vessels that are diseased, and a method and apparatus for delivery and implantation of the stents.
Stents conventionally repair blood vessels that are diseased. Stents are generally hollow and cylindrical in shape and have terminal ends that are generally perpendicular to their longitudinal axis. In use, the conventional stent is positioned at the diseased area of a vessel and, after deployment, the stent provides an unobstructed pathway for blood flow.
Repair of vessels that are diseased at a bifurcation is particularly challenging since the stent must be precisely positioned, provide adequate coverage of the disease, provide access to any diseased area located distal to the bifurcation, and maintain vessel patency in order to allow adequate blood flow to reach the myocardium. Therefore, the stent must provide adequate coverage to the diseased portion of the bifurcated vessel, without compromising blood flow, and extend to a point within and beyond the diseased portion. Where the stent provides coverage to the vessel at the diseased portion, yet extends into the vessel lumen at the bifurcation, the diseased area is repaired, but blood flow may be compromised in other portions of the bifurcation. Unapposed stent elements may promote lumen compromise during neointimal formation and healing, producing restenosis and requiring further procedures. Moreover, by extending into the vessel lumen at the bifurcation, the stent may block access to further interventional procedures.
Conventional stents are designed to repair areas of blood vessels that are removed from bifurcations, and, therefore are associated with a variety of problems when attempting to use them to treat lesions at a bifurcation. Conventional stents are normally deployed so that the entire stent is either in the parent vessel or the proximal portion of the stent is in the parent vessel and the distal portion is located in the side branch vessel. In both cases, either the side branch vessel (former case) or the parent vessel (later case), would become xe2x80x9cjailedxe2x80x9d by the stent struts. This technique repairs one vessel at the bifurcation at the expense of jailing or obstructing the alternate vessel. Blood flow into the jailed vessel would be compromised as well as future access and treatment into the distal portion of the jailed vessel.
Alternatively, access into a jailed vessel can be attained by carefully placing a guide wire through the stent, and subsequently tracking a balloon catheter through the stent struts. The balloon could then be expanded, thereby deforming the stent struts and forming an opening into the previously jailed vessel. The cell to be spread apart must be randomly and blindly selected by re-crossing the deployed stent with a guide wire. The drawback with this approach is that there is no way to determine or guarantee that the main-vessel stent struts are properly oriented with respect to the side branch or that an appropriate stent cell has been selected by the wire for dilatation. The aperture created often does not provide a clear opening and creates a major distortion in the surrounding stent struts. A further drawback with this approach is that there is no way to tell if the main-vessel stent struts have been properly oriented and spread apart to provide a clear opening for stenting the side branch vessel. This technique also causes stent deformation to occur in the area adjacent to the carina, pulling the stent away from the vessel wall and partially obstructing flow in the originally non-jailed vessel. Deforming the stent struts to regain access into the previously jailed strut is also a complicated and time consuming procedure associated with attendant risks to the patient and is typically performed only if considered an absolute necessity. Vessels which supply a considerable amount of blood supply to the myocardium and may be responsible for the onset of angina or a myocardial infarct would necessitate the subsequent strut deformation in order to reestablish blood flow into the vessel. The risks of procedural complications during this subsequent deformation are considerably higher than stenting in normal vessels. The inability to place a guide wire through the jailed lumen in a timely fashion could restrict blood supply and begin to precipitate symptoms of angina or even cardiac arrest. In addition, platelet agitation and subsequent thrombus formation at the jailed site could further compromise blood flow into the side branch.
Plaque shift is also a phenomena which is of concern when deploying a stent across a bifurcation. Plaque shift occurs when treatment of disease or plaque in one vessel causes the plaque to shift into another location. This is of greatest concern when the plaque is located on the carina or the apex of the bifurcation. During treatment of the disease the plaque may shift from one side of the carina to the other thereby shifting the obstruction from one vessel to the alternate vessel.
In another prior art method of implanting stents, a xe2x80x9cTxe2x80x9d stent procedure includes implanting a stent in the side branch ostium of the bifurcation followed by stenting the main vessel across the side branch and subsequently deforming the struts as previously described, to allow blood flow and access into the side branch vessel. Alternatively, a stent is deployed in the parent vessel and across the side branch origin followed by subsequent strut deformation as previously described, and finally a stent is placed into the side branch vessel. T stenting may be necessary in some situations in order to provide further treatment and additional stenting in the side branch vessel. This is typically necessitated when the disease is concentrated at the origin of the jailed vessel. This procedure is also associated with the same issues and risks previously described when stenting only one vessel and deforming the struts through the jailed vessel. In addition, since a conventional stent generally terminates at right angles to its longitudinal axis, the use of conventional stents to treat the origin of the previously jailed vessel (typically the side branch vessel) may result in blocking blood flow of the originally non-jailed vessel (typically the parent vessel) or fail to provide adequate coverage of the disease in the previously jailed vessel (typically a side branch vessel). The conventional stent might be placed proximally in order to provide full coverage around the entire circumference of the side branch, however this leads to a portion of the stent extending into the pathway of blood flow of the parent vessel. The conventional stent might alternatively be placed distally to, but not entirely overlaying the circumference of the origin of the side branch to the diseased portion. Such a position of the conventional stent results in a bifurcation that does not provide full coverage or has a gap on the proximal side (the origin of the side branch) of the vessel and is thus not completely repaired. The only conceivable situation that the conventional stent, having right-angled terminal ends, could be placed where the entire circumference of the ostium is repaired without compromising blood flow, is where the bifurcation is formed of right angles. In such scenarios, extremely precise positioning of the conventional stent is required. This extremely precise positioning of the conventional stent may result with the right angled terminal ends of the conventional stent overlying the entire circumference of the ostium to the diseased portion without extending into a side branch, thereby repairing the right-angled bifurcation.
To circumvent or overcome the problems and limitations associated with conventional stents in the context of repairing diseased bifurcated vessels, a stent that consistently overlays most of the diseased area of the bifurcation and provides adequate access to distal disease without subjecting the patient to any undue risks may be employed. Such a stent would have the advantage of providing adequate coverage at the proximal edge of the origin of the side branch such that a conventional stent which terminates at right angles to its longitudinal axis can be deployed in the side branch or alternate vessel without leaving a significant gap at the origin of the side branch. In addition, such a stent would allow access to all portions of the bifurcated vessel should further interventional treatment be necessary.
In another prior art method for treating bifurcated vessels, commonly referred to as the xe2x80x9cCulotte technique,xe2x80x9d the side branch vessel is first stented so that the stent protrudes into the main or parent vessel. A dilatation is then performed in the main or parent vessel to open and stretch the stent struts extending across the lumen from the side branch vessel. Thereafter, a stent is implanted in the side branch so that its proximal end overlaps with the parent vessel. One of the drawbacks of this approach is that the orientation of the stent elements protruding from the side branch vessel into the main vessel is completely random. In addition excessive metal coverage exists from overlapping strut elements in the parent vessel proximal to the carina area. Furthermore, the deployed stent must be recrossed with a wire blindly and arbitrarily selecting a particular stent cell. When dilating the main vessel the stent struts are randomly stretched, thereby leaving the possibility of restricted access, incomplete lumen dilatation, and major stent distortion.
In another prior art procedure, known as xe2x80x9ckissingxe2x80x9d stents, a stent is implanted in the main vessel with a side branch stent partially extending into the main vessel creating a double-barrelled lumen of the two stents in the main vessel distal to the bifurcation. Another prior art approach includes a so-called xe2x80x9ctrouser legs and seatxe2x80x9d approach, which includes implanting three stents, one stent in the side branch vessel, a second stent in a distal portion of the main vessel, and a third stent, or a proximal stent, in the main vessel just proximal to the bifurcation.
All of the foregoing stent deployment assemblies suffer from the same problems and limitations. Typically, there is uncovered intimal surface segments on the main vessel and side branch vessels between the stented segments or there is excessive coverage in the parent vessel proximal to the bifurcation. An uncovered flap or fold in the intima or plaque will invite a xe2x80x9csnowplowxe2x80x9d effect, representing a substantial risk for sub-acute thrombosis, and the increased risk of the development of restenosis. Further, where portions of the stent are left unapposed within the lumen, the risk for subacute thrombosis or the development of restenosis again is increased. The prior art stents and delivery assemblies for treating bifurcations are difficult to use and deliver making successful placement nearly impossible. Further, even where placement has been successful, the side branch vessel can be xe2x80x9cjailedxe2x80x9d or covered so that there is impaired access to the stented area for subsequent intervention. The present invention solves these and other problems as will be shown.
In addition to problems encountered in treating disease involving bifurcations for vessel origins, difficulty is also encountered in treating disease confined to a vessel segment but extending very close to a distal branch point or bifurcation which is not diseased and does not require treatment. In such circumstances, very precise placement of a stent covering the distal segment, but not extending into the distal side branch, may be difficult or impossible. The present invention also offers a solution to this problem.
The invention provides for improved stent designs and stent delivery catheter assemblies for repairing a main vessel and side branch-vessel forming a bifurcation, without compromising blood flow, thereby allowing access to all portions of the bifurcated vessels should further interventional treatment be necessary. The present invention includes a trap-door stent pattern, a stent delivery catheter assembly, an apparatus for crimping the stent and the method for crimping the stent onto the catheter, and the method for delivering and implanting the stent in a bifurcated vessel.
The Stent Pattern
The stent of the present invention includes a cylindrical body having rings aligned along a longitudinal axis, where each ring has a delivered diameter in which it is crimped or compressed tightly onto the balloon catheter, and an implanted diameter where the stent is implanted in a bifurcated vessel. Each ring also includes a number of first peaks that are configured to spread apart to permit the rings to be greatly expanded outwardly or to be compressed radially inwardly onto the balloon portion of a delivery catheter. In one embodiment, the cylindrical body includes a proximal section, a distal section, and a central section. The proximal section includes between one and fifteen rings, the distal section includes between one and fifteen rings, and the central section includes between one and ten rings. In one embodiment, the number of first peaks in the central section differs from the number of first peaks in the proximal section and the distal section. In another embodiment, the rings of the proximal section have between four and twelve first peaks, the rings of the distal section have between four and twelve first peaks, and the rings of the central section have between five and fifteen first peaks. In another embodiment of the stent, the rings of the proximal section have seven first peaks, the rings of the distal section have six first peaks, and the rings of the central section have eight first peaks. In another embodiment, the number of first peaks in the rings or ring of the central section is greater than the number of first peaks in any of the rings of either the proximal section or the distal section. In each of the embodiments, the rings are connected by at least one link between adjacent rings.
In one embodiment of the stent of the invention, the proximal section, the distal section, and the central section each have only one ring. In this embodiment, the stent is highly deliverable since it will typically be substantially shorter than a stent having a greater number of rings, so that it can pass through tortuous anatomy more easily and rotational position of the stent is easily achieved by applying torque to the delivery system or manipulating the guide wires.
In one embodiment of the stent of the invention, the rings in the central section of the stent have a corresponding set of nested peaks that are nested within the first peak of the rings of the central section. The nested peaks, when expanded, will appose the opening to the side branch vessel and provide additional support and vessel wall coverage. With the addition of the nested peaks, the central section of the stent can expand to an even greater diameter than a similar stent without the nested peaks because the nested peaks provide more material to expand.
The links connecting the rings can have various embodiments including straight segments, curved segments, undulating segments, and non-linear segments.
The tubular body of the stent of the invention has a distal opening, a proximal opening, and a central opening. The distal opening and the proximal opening are aligned along the stent longitudinal axis and typically would be implanted in the main vessel, while the central opening is radially offset relative to the alignment of the distal opening and the proximal opening. The stent is implanted so that the central opening provides access to the side branch (or alternative vessel) and the ring or rings proximal to the central opening provide support and coverage to the origin of the side branch and to the area immediately proximal to the carina.
Each ring of the stent of the present invention has at least one second peak where at least some of the at least one second peaks is connected to a link.
The stent of the present invention includes struts that make up the rings and links, the struts having either uniform cross-sections, or cross-sections having various widths and thicknesses.
The Stent Delivery Catheter
The present invention also includes a stent delivery catheter assembly for repairing bifurcated vessels including an elongated catheter body which has a proximal catheter shaft, an intermediate section or mid-section, and a distal section. The catheter assembly contains an over-the-wire (OTW) guide wire lumen extending from the proximal catheter hub to one of the distal tips of the distal end of the catheter. The catheter assembly also includes a rapid exchange (Rx) guide wire lumen which extends from the proximal end of the mid-section to one of the distal tips of the distal end of the catheter. The proximal catheter shaft also contains an inflation lumen which extends from the proximal hub of the proximal catheter shaft to the mid-section of the catheter and is in fluid communication with the inflation lumen contained within the mid-section. The mid-section contains lumens for both an OTW and an Rx guide wire lumen. The Rx guide wire lumen begins at about the proximal section of the intermediate shaft and extends to one of the distal tips of the distal catheter shaft. The OTW guide wire lumen extends through the intermediate section of the catheter and extends proximally to the catheter hub connected to the proximal catheter shaft and extends distally to one of the tips of the distal section of the catheter. The distal section of the catheter consists of two shafts extending from the distal end of the mid-shaft to the distal end of the catheter tips. Each shaft has a balloon connected adjacent the distal end followed by a tip connected to the distal end of the balloon. Each shaft contains a guide wire lumen and an inflation lumen. The inflation lumen of each shaft is in fluid communication with the inflation lumen of the mid-shaft. One of the shafts of the distal section contains an Rx guide wire lumen, which extends proximally through the mid-section of the catheter and exits at about the proximal end of the mid-section of the catheter, the Rx guide wire lumen also extends distally to one of the tips of the distal section of the catheter. The second shaft of the distal section contains an OTW guide wire lumen, which extends proximally through the mid-section and proximal section of the catheter and exits at the proximal hub connected to the distal end of the proximal catheter section, the OTW guide wire lumen also extends distally to one of the tips of the distal section of the catheter. The distal section of the catheter includes two balloons. One balloon is longer and is connected to one of the shafts of the distal catheter section. The long balloon is connected to the catheter shaft such that the inflation lumen of the shaft is in fluid communication with the balloon and the guide wire lumen contained within the shaft extends through the center of the balloon. The proximal section of the balloon is sealed to the distal end of the shaft and the distal end of the balloon is sealed around the outside of the guide wire lumen or inner member running through the center of the balloon. The proximal and distal seals of the balloon allow for fluid pressurization and balloon inflation from the proximal hub of the catheter. The short balloon is connected in the same manner as the long balloon described above to the alternate shaft of the distal section of the catheter. Each balloon has a tip extending from their distal ends. The tips are extensions of the inner members extending through the center of the balloon and contain a lumen for a guide wire associated with each guide wire lumen. The distal end of the catheter has two tips associated with their respective balloons and the guide wire lumen or inner member. One tip is longer and contains a coupler utilized for joining the tip during delivery of the previously described stent.
The stent of the present invention is crimped or compressed onto the long balloon and the short balloon such that the long balloon extends through the distal opening and the proximal opening in the stent, while the short balloon extends through the proximal opening and the central opening of the stent.
In one embodiment of the bifurcated catheter assembly, the OTW guide wire lumen extends through the short balloon and the short tip. The OTW guide wire and short balloon are configured for treating the side branch or alternate vessel. The Rx guide wire lumen extends through the long balloon and the long tip and coupler. The Rx guide wire and the long balloon and long tip are configured for treating the parent or main vessel. The coupler consists of a joining lumen adjacent to and connected to the long tip. The lumen extends from the proximal end of the long tip and extends between 1 mm to about 20 mm to the end of the long tip where it terminates. The proximal end of the joining lumen is located distal to the position of the short tip. A joining wire extends through the proximal hub and distally exits the short tip and then enters the joining lumen of the coupler on the long tip thereby joining the two tips. The proximal hub has a mechanism which locks the joining wire into position while the catheter and stent are tracked into position. The wire can then be released or unlocked at the appropriate time and retracted to release or uncouple the tips. The locking mechanism on the proximal hub is similar to a Rotating Hemostatic Valve (RHV) mechanism which consists of a two part housing with an O ring inside. The two part housing has one piece with male threads and another with female threads. The housing is screwed together until compression is applied to the O ring causing the inside diameter of the O ring to continually decrease until it locks onto the joining wire. Alternatively, the OTW guide wire can be used as the joining wire.
In another embodiment of the bifurcated catheter assembly, the long tip contains a series of holes on the distal section of the long tip and the short tip contains a series of holes on the distal section of the short tip. The holes are aligned and spaced on the long and short tip such that a staggered relationship between hole pairs is created between the holes on the long and short tip. The tips are then coupled by a joining wire which is threaded through the staggered hole pairs in the distal section of the long and short tips. The joining wire extends proximally through the OTW guide wire lumen to the proximal hub where it is locked in place as previously described. The Rx guide wire extends through the Rx guide wire lumen proximally through the center of the long balloon and exits the Rx notch located on the mid-section of the catheter and extends distally through the long tip and into the distal anatomy. The diameter of the joining wire is such that it occupies minimal space in the Rx guide wire lumen and does not create interference with the Rx guide wire. The tips are uncoupled at the appropriate time by unlocking the joining wire and removing it from the anatomy.
In another embodiment of the bifurcated catheter assembly, the OTW guide wire lumen extends through the long tip and coupler, and the long tip is connected to the short balloon. The OTW guide wire lumen and short balloon are configured for treatment of the side branch or alternate vessel. The OTW guide wire lumen extends to the proximal hub of the proximal section of the catheter. The Rx guide wire lumen extends through the long balloon and short tip distally and extends proximally to the exit notch located on the mid-section of the catheter. The Rx guide wire lumen and long balloon are configured to treat the parent or main vessel. The coupler consists of a joining lumen adjacent to and attached to the distal end of the long tip. The proximal end of the joining lumen is located distal to the short tip and the distal end of the joining lumen extends slightly beyond the long tip. The end of the joining lumen is open and the Rx guide wire extends distally through the joining lumen and into the distal anatomy and extends proximally through the short tip and long balloon to the exit notch located on the mid-section of the catheter. The OTW guide wire extends from the distal end of the long tip to the proximal hub located on the proximal section of the catheter. The tips are uncoupled at the appropriate location and time during the procedure by retracting the Rx guide wire such that the tip of the wire exits the coupling lumen located in the distal section of the Rx tip.
In another embodiment of the bifurcated catheter assembly, the long tip contains a slit used for coupling the two tips together. The Rx guide wire extends through the Rx guide wire lumen contained in the short tip and extends proximally through the center of the long balloon and exits the Rx guide wire exit notch located on the mid-section of the catheter. The Rx guide wire extends distally through the Rx guide wire lumen and exits the short tip and then enters the distal section of long tip through the slit. The Rx guide wire exits the long tip and continues distally through the anatomy. The OTW guide wire extends from the distal end of the long tip to the proximal hub located on the proximal section of the catheter. The tips are uncoupled at the appropriate location and time during the procedure by retracting the Rx guide wire such that the tip of the wire exits the slit located in the distal section of the long tip.
In another embodiment of the bifurcated catheter assembly, the long tip contains two slits on the distal section of the long tip. The Rx guide wire extends through the Rx guide wire lumen contained in the short tip and extends proximally through the center of the long balloon and exits the Rx guide wire exit notch located on the mid-section of the catheter. The Rx guide wire extends distally through the Rx guide wire lumen and exits the short tip and then enters the distal section of long tip through one of the slits. The Rx guide wire exits the long tip and continues distally through the anatomy. The OTW guide wire extends from the distal end of the long tip to the proximal hub located on the proximal section of the catheter. The tips are uncoupled at the appropriate location and time during the procedure by retracting the Rx guide wire such that the tip of the wire exits the slit located in the distal section of the long tip. Before the tips are uncoupled, the OTW guide wire is advanced through the long tip and exits the alternate slit and continues into the distal anatomy. Advancement of the OTW guide wire before retracting the Rx guide wire for uncoupling always ensures wire placement in the distal and diseased anatomy. Maintaining a wire in the distal and diseased anatomy ensures access to the vessel in the event of vessel closure due to vessel dissection or spasm.
In another embodiment of the bifurcated catheter assembly, the long tip contains a slit in the distal section of the long tip and is configured to allow the inner diameter of the lumen to expand when an outward radial force is applied (by a guide wire pushed from the proximal end) and contract to its original shape when the guide wire is removed. The tip is formed from a material having elastic and retractable properties such as found in a variety of elastomers. An expandable pattern such as minute cuts or slits, can then be cut (with a laser) in the distal section of the long tip. The expandable pattern contains elements which deform when an outward radial force is applied to the inside of the lumen. The elements then return to their original shape when the outward radial force is removed. An alternate method of creating an expandable tip would be to utilize a more conventional tip or inner member material, and then subsequently cut an expandable pattern (slits) in the distal section of the tip. An additional material with the appropriate elastic and retractable properties can then be coated or bonded over the distal section of the long tip to impart the expandable properties of the tip. The Rx guide wire extends through the Rx guide wire lumen contained in the short tip and extends proximally through the center of the long balloon and exits the Rx guide wire exit notch located on the mid-section of the catheter. The Rx guide wire extends distally through the Rx guide wire lumen and exits the short tip and then enters the distal section of long tip through the slit. The Rx guide wire exits the long tip and continues distally through the anatomy. The OTW guide wire extends from the distal end of the long tip to the proximal hub located on the proximal section of the catheter. During delivery of the stent, the distal end of the OTW guide wire remains in the distal section of the long tip just proximal of the slit. Before the tips are uncoupled, the OTW guide wire is advanced through the long tip which will expand upon advancement of the OTW guide wire since both of the guide wires will exit through the portion of the long tip distal of the slit. The tips are then uncoupled at the appropriate location and time during the procedure by retracting the Rx guide wire such that the tip of the wire exits the slit located in the distal section of the long tip.
The present invention also includes a stent delivery catheter assembly for repairing bifurcated vessels including an elongated catheter body which has a proximal end and a distal end and a proximal catheter shaft and an over-the-wire (OTW) guide wire lumen extending therethrough. The catheter assembly also includes a rapid exchange (Rx) catheter portion attached to the distal end of the proximal catheter shaft, the Rx catheter portion having a distal end and a proximal end with an Rx guide wire lumen extending therethrough and a coupler associated with the distal end of the Rx catheter portion. The catheter body also includes an OTW catheter portion attached to the distal end of the proximal catheter shaft, where the OTW catheter portion includes an OTW guide wire lumen that corresponds with and aligns with the OTW guide wire lumen in the proximal catheter shaft. A long balloon is associated with the Rx catheter portion and a short balloon is associated with the OTW catheter portion. The Rx catheter portion is configured for treating the main vessel of a bifurcation and the OTW catheter portion is configured for treating a side branch vessel of the bifuircation. Alternatively, the OTW catheter portion is configured for treating the main vessel of a bifurcation, while the Rx catheter portion is configured for treating a side branch vessel of the bifurcation. The stent of the present invention is crimped or compressed onto the long balloon and the short balloon such that the long balloon extends through the distal opening and the proximal opening in the stent, while the short balloon extends through the proximal opening and the central opening of the stent.
In another embodiment of the bifurcated catheter assembly of the invention, the bifurcated catheter can be used for a variety of procedures such as dilatation, drug delivery, and delivering and deploying the stent of the invention in a body lumen. The bifurcated catheter assembly includes an elongated shaft having a proximal shaft section with a first inflation lumen and a multifurcated distal shaft section with a first branch and at least a second branch. The first branch has a second inflation lumen with at least a portion thereof in fluid communication with the first inflation lumen. An intermediate shaft section joins the proximal and distal sections together and defines a fourth inflation lumen in fluid communication with the first, second and third inflation lumens. A joining wire lumen extends within the proximal section, the intermediate section, and the first branch of the multifurcated distal section. The guide wire lumen extends within the intermediate section and the second branch of the multifurcated distal section. The guide wire lumen extends within the intermediate section and the second branch of the multifurcated distal section. A first balloon is positioned on the first branch and a second balloon is positioned on the second branch, with interiors of the balloons in fluid communication with the inflation lumens. A coupler is associated with the second branch, distal to the second balloon, and is configured for releasably coupling the first and second branches together to form a coupled configuration.
The Stent Crimping Method
The stent of the present invention can be tightly crimped or compressed onto the catheter assembly so that the stent remains firmly in place until the balloons are expanded, thereby expanding the stent at the site of the bifurcation. In keeping with the invention, a mold assembly is provided for use in progressively crimping the stent in a tighter and tighter configuration until it is tightly crimped or compressed onto the long and short balloons of the catheter assembly. In one embodiment, the crimping assembly or mold assembly includes three sections, including a tapered section, a straight section, and a finish section, through which the stent, which has been premounted on the balloons, is advanced for the purpose of progressively compressing the stent onto the balloons. The tapered section of the mold assembly has a tapered lumen and an opening or first end in which its cross-section is larger than the cross-section of the uncrimped stent premounted on the balloons of the catheter assembly. The tapered section has a second end having a smaller cross-section than the first end so that as the stent and balloons are advanced through the tapered section and its tapered lumen, the stent will be progressively compressed onto the balloons so that the stent will take substantially the same shape as the cross-section of the second end of the tapered section. The straight section has a first end cross-section that is basically the same size cross-section as the second end of the tapered section, and the straight section also has a second end cross-section that is substantially the same size cross-section as the first end. The stent and balloons are advanced through the straight section to provide a uniform crimp along the stent surface so that any unevenness created by the tapered lumen of the tapered section is removed, thereby providing a smooth and uniform stent outer surface having a configuration shaped substantially like the lumen defined by the second end of the straight section. The stent and balloons are then advanced through the finish section which has a first end cross-section that is substantially the same cross-sectional shape as the second end of the straight section. As the stent and balloons are advanced through the finish section, they are progressively compressed or crimped into the cross-sectional configuration of the second end of the finish section. After the stent and catheter have been successfully inserted into the mold, the balloons can be pressurized and heat can be applied to the mold to further enhance the stent retention. The result is a tightly crimped stent on the long and short balloons so that the stent will remain firmly attached to the long and short balloons during delivery of the stent through tortuous vessels such as the coronary arteries. Once the stent and long balloons are positioned at the bifurcations, the balloons can be inflated as will be hereinafter described, to expand the stent and implant it at the bifurcation.
Delivering and Implanting the Stent
The method of delivering and implanting the stent mounted on the catheter assembly are contemplated by the present invention. The bifurcated catheter assembly of the present invention provides two separate balloons in parallel which are advanced into separate passageways of an arterial bifurcation and the balloons are inflated either simultaneously or independently (or a combination thereof) to expand and implant the stent. More specifically, and in keeping with the invention, the catheter assembly is advanced through a guiding catheter (not shown) until the distal end of the catheter assembly reaches the ostium to the coronary arteries. An Rx guide wire is advanced out of the Rx shaft and into the coronary arteries to a point distal of the bifurcation or target site. In a typical procedure, the Rx guide wire will already be positioned in the main vessel after a pre-dilatation procedure. The catheter assembly is advanced over the Rx guide wire so that the catheter distal end is just proximal to the opening to the side branch vessel. Up to this point in time, the OTW guide wire (or mandrel or joining wire) remains within the catheter assembly and within the coupler so that the long balloon and the short balloon of the catheter assembly remain adjacent to one another to provide a low profile. As the catheter assembly is advanced to the bifurcated area, the coupler moves axially relative to the distal end of the OTW guide wire (or mandrel or joining wire) a small distance (approximately 0.5 mm up to about 5.0 mm), but not pull completely out of the coupler, making it easier for the distal end of the catheter to negotiate tortuous turns in the coronary arteries. Thus, the slight axial movement of the coupler relative to the OTW guide wire (or mandrel or joining wire) distal end allows the tips to act or move independently, thereby increasing flexibility over the tips joined rigidly and it aids in the smooth tracking of the catheter assembly over the Rx guide wire. The proximal end of the OTW guide wire is releasably attached to the proximal hub as previously described. The OTW guide wire (or mandrel or joining wire) is removed or withdrawn proximally from the coupler, thereby uncoupling the long balloon and the short balloon. Thereafter, the OTW guide wire is advanced distally into the side branch vessel so that the catheter assembly can next be advanced distally over the Rx guide wire in the main vessel and the OTW guide wire in the side branch vessel. The separation between the Rx guide wire and the OTW guide wire allows the long balloon and the short balloon to separate slightly as the catheter assembly is further advanced over the Rx guide wire and the OTW guide wire. The catheter assembly advances distally until it reaches a point where the central opening on the stent is approximately adjacent to the opening to the side branch vessel, so that the catheter assembly can no longer be advanced distally since the stent is now pushing up against the opening to the side branch vessel. One or more radiopaque markers are placed on the distal portion of the catheter assembly to aid in positioning the stent with respect to the bifurcation or target site. Once the long and short balloons with the stent mounted thereon are positioned in the main vessel just proximal to the side branch vessel, the long balloon and the short balloon are next inflated simultaneously or independently (or a combination thereof), to expand the stent in the main vessel and the opening to the side branch vessel. The central section of the stent is expanded into contact with the opening to the side branch vessel and the central opening should substantially coincide with the opening to the side branch vessel providing a clear blood flow path through the proximal opening of the stent and through the central opening into the side branch vessel. By inflating the long balloon and the short balloon substantially simultaneously, plaque shifting is avoided and better vessel wall coverage results.
As the catheter assembly is advanced through tortuous coronary arteries, over the Rx guide wire, the central opening of the stent may or may not always be perfectly aligned with the opening to the side branch vessel. If the central opening of the stent is in alignment with the opening to the side branch vessel it is said to be xe2x80x9cin phasexe2x80x9d and represents the ideal position for stenting the main branch vessel and the opening to the side branch vessel. When the central opening of the stent and the opening to the side branch vessel are not aligned it is said to be xe2x80x9cout of phasexe2x80x9d and depending upon how many degrees out of phase, the stent may require repositioning or reorienting so that the central opening more closely coincides with the opening to the side branch vessel. The orientation of the central opening of the stent with respect to the opening to the side branch vessel can range anywhere from a few degrees to 360xc2x0. If the central opening of the stent is more than 90xc2x0 out of phase with respect to the opening to the side branch vessel, it may be difficult to position the radiopaque marker, and thus the linear or longitudinal position of the stent. When the central opening is in the out of phase position, the stent of the invention still can be implanted and the central opening will expand into the opening of the side branch vessel and provide adequate coverage. In cases where the system is more than 90xc2x0 out of phase, the Rx and OTW guide wires will be crossed causing a distal torque to be applied to help the system to rotate in phase. In the event rotation does not occur, the system can be safely deployed with adequate coverage and support as long as the radiopaque markers located on the distal end of the catheter reach the proper positioning as can be detected under fluoroscopy. The unique and novel design of the catheter assembly and the stent of the present invention minimizes the misalignment so that the central opening of the stent generally aligns with the opening to the side branch vessel, and is capable of stenting the opening to the side branch vessel even if the central opening is out of phase from the opening of the side branch vessel.
After the stent of the present invention has been implanted at the bifurcation, if necessary a second stent can be implanted in the side branch vessel so that the second stent abuts the central opening of the stent of the present invention.